Call Clearing for legacy mobile circuit switched domain wireless systems

ABSTRACT

A telecommunications system having a first PS network, second PS network and a third circuit-switched core network includes a system for terminating a legacy domain circuit-switched communication upon receipt of a trigger signal requesting termination of communication. The system includes first and second functional entities in each network. The first and second functional entities of the first network can communicate signals over an interface using a PS protocol. The first and second functional entities of the second network include can communicate signals over an interface using a PS protocol. The first functional entity of the first network can communicate packet data to and from the first functional entity of the second network. The second functional entity of the first network communicates a PS protocol signal to the second entity of the second network, which then communicates a circuit-switched protocol signal to and from the third circuit-switched protocol core network to terminate the circuit-switched communication.

CROSS-REFERENCED APPLICATION

[0001] This application relates to co-pending U.S. provisional patentapplication Serial No. 60/362,613, filed Mar. 8, 2002, and entitled“Call Clearing for LMSD,” the contents of which are incorporated byreference.

FIELD OF THE INVENTION

[0002] The present invention relates to call clearing in a mobilenetwork while interworking between a legacy circuit-switched domain anda packet-switched domain.

BACKGROUND

[0003] In circuit-switched (CS) mobile telecommunications systems, amobile station (MS) sends a signal or message, which is picked up by abase transmitting station (BTS) and then routed by a base stationcontroller (BSC). The signal or message is forwarded by the BSC to anassociated mobile switching center (MSC), for routing to the appropriatedestination, for example, a public switched telephone network, PSTN, orother telecommunications node or network.

[0004] To increase multimedia and Internet capabilities, and for otherreasons, most mobile telecommunications systems are being migrated fromuse of a circuit-switched core network to use of a packet-switched (PS)protocol network. Systems using a PS network nevertheless typicallyneeds support for handling calls routed through non-PS systems (forexample, PSTN). Ideally, support for existing mobile stations (MS's),for example, call initiation, call termination, in a PS signalingnetwork environment will operate in a manner transparent to the user.Furthermore, ideally, such support should also permit supporting newfeatures and capabilities. However, end users are often stymied by alack of standardization to enable such migration from circuit-switchednetworks to packet-switched mobile networks to continue.

[0005] Therefore, what is needed is a method for call clearing between acircuit switched network and a PS network for communicating with amobile station.

SUMMARY OF THE INVENTION

[0006] A telecommunications system is provided having at least a firstPS network, a second PS network, a third circuit-switched core network,and a system for terminating a legacy domain circuit-switchedcommunication upon receipt of a trigger signal requesting termination ofcommunication. The system for terminating a legacy domaincircuit-switched communication comprises a first functional and a secondfunctional entity in each of the first and second networks, the firstfunctional entity and the second functional entity of the first networkincluding means for communicating signals over an interface using a PSprotocol. The first functional entity and the second functional entityof the second network include means for communicating signals over aninterface using a PS protocol, the first functional entity of the firstnetwork having means for communicating packet data to and from the firstfunctional entity of the second network, the second functional entity ofthe first network having means for communicating a PS protocol signal tothe second entity of the second network. The second functional entity ofthe second network further includes means for communicating acircuit-switched protocol signal to and from the third circuit-switchedprotocol core network to terminate the circuit-switched communication.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] For a more complete understanding of the present invention, andthe advantages thereof, reference is now made to the followingdescription taken in conjunction with the accompanying drawings, inwhich:

[0008]FIG. 1 is a functional block diagram depicting a PS network,having a Legacy Mobile Station Domain Support (LMSDS), in communicationwith another PS network having a LMSDS;

[0009]FIG. 2 is a block diagram depicting a protocol stack for referencepoint zz of FIG. 1; and

[0010]FIG. 3 is a node diagram depicting an example of call clearinginitiated by the based station, and

[0011]FIG. 4 is a node diagram depicting an example of call clearinginitiated by a signaling message sent from the PSTN.

DETAILED DESCRIPTION

[0012] Turning now to FIG. 1, a system for handling circuit-switchedoperations in a telecommunications system having a PS network isdepicted. In the following discussion, numerous specific details are setforth to provide a thorough understanding of the present invention.However, it will be obvious to those skilled in the art that the presentinvention can be practiced without such specific details. In otherinstances, well-known elements have been illustrated in schematic orblock diagram form in order not to obscure the present invention inunnecessary detail. Additionally, for the most part, details concerningCDMA systems and the like have been omitted inasmuch as such details arenot considered necessary to obtain a complete understanding of thepresent invention, and are considered to be within the skills of personsof ordinary skill in the relevant art.

[0013] It is further noted that, unless indicated otherwise, allfunctions described herein are performed by a processor such as acomputer or electronic data processor in accordance with code such ascomputer program code, software, and/or integrated circuits that arecoded to perform such functions.

[0014]FIG. 1 illustrates first and second PS networks 1 and 2 incommunication with one another across reference points yy and zz.Network 1 includes Legacy Mobile Station Domain Support (LMSDS) 11,which includes a home location register emulator (HLRe) 15 and a PS callcontrol entity, such as a mobile switching control emulator (MSCe) 17.An LMSDS can be generally defined as support for allowing a standardizedconversion between circuit-switched data and packet-switched data fortransmission on a mobile network.

[0015] In FIG. 1, for forward and backward compatibility purposes (forexample, to allow PS performance in telecommunications services withoutsacrificing the requirement for the transparent handling of legacycircuit-switched MS calls), the functionality of a circuit-switched MSCis divided into two functionally distinct entities. One functionallydistinct entity is the MSCe 17, which is responsible for call signaling,both for packet and non-packet communications. Signaling can begenerally defined as the determination of the routing path from oneentity to another entity. Another functionally distinct entity is theMGW 7, which is responsible for the transmission of the bearer traffic.Bearer traffic can be generally defined as the data that is routed bythe signaling. The MSCe 17 is the control entity that converts non-PScall signaling (for example, PSTN) to PS call signaling (andvice-versa), and controls the call routing through the PS network 1 andinteracts with the MGW 47 of the network 2.

[0016] The division of functions into separate functional entitiesseparated by a PS protocol interface facilitates the use of openstandards for managing traffic and signals in a PS environment, such asMegaco, SIP, IOS, and circuit-switched signal protocols such as SS7. Thepresent invention facilitates specific functionality within the MSCe,between the MSCe and the MGW and among other MSCe's on other networks.In FIG. 1, network 2 has the LMSDS 12, which includes an HLRe 31, and anMSCe 45, which controls its MGW 47.

[0017] The MGW 7 has an interface between the packet environment of thePS network 1 and the circuit switched environment of the PSTN 44 forbearer traffic, when equipped with circuit capabilities. The MGW 7 canprovide vocoding and/or transcoding functions to the bearer traffic. TheMGW 7 can also provide modem functions to convert digital byte streamsto and from audio modem tones placed on circuits, and can provide thecapability to terminate Point-to-Point Protocol (PPP) connections. Italso provides policy enforcement relative to its activities andresources.

[0018] The MGW 7 supports the bearer aspects and bearer switchingfabric, tone, announcement and bridging capabilities. In addition, theMGW 7 supports the PS bearer for actual call delivery to other LMSDS'sacross reference point/interface yy and provides bearer support forconnectivity to the PSTN 44. The MGW 7 can use PS protocol signalingfrom the MSCe 17 for tones and announcements control, for bearerestablishment and bridging control functions. In FIG. 1, the LMSDS 11 isemployable to provide support for the following interfaces; MGW to radioaccess network (RAN) voice bearer (27), MGW to RAN circuit data bearer(27), MGW to PSTN Bearer (34), MSCe 17 to MGW 7 signaling (39), and MGWto MGW PS bearer (yy). An access network, such as access network 42 or43, can comprise a base station, and can be part of the RAN.

[0019] The MGW 7 also can have the following capabilities: It terminatesbearer channels from the PSTN 44 on interface 34, bearer channels fromthe radio network on interfaces 27 and media streams from a packetnetwork on interface yy; it supports voice and circuit data mediastreams on these network terminations; it provides switching of thebearer channels by connecting media streams from one set of networkterminations to another set of network terminations; and it convertsmedia in one type of network termination to the format required inanother type of network termination.

[0020] The MGW 7 has the ability to connect to the PS protocolenvironment of another PS network, for example, network 2, as well asthe circuit-based environment of the PSTN 44. Therefore, the resourcesprovided by the MGW 7, including transcoding resources, can be used tosupport bearer channels that are contained entirely within the PSenvironment.

[0021] The MGW 7 supports conversion of a non-PS traffic bearer to a PStraffic bearer and transports the PS traffic bearer to the finaldestination and vice versa. In other words, the MGW 7 performs theactual encapsulation between circuit-switched data to packet-switcheddata, and the MSCe 15 performs the mapping of the routing informationbetween circuit-switched data and packet-switched data. To perform itsfunctions, the MSCe 17 can be capable of communicating with the PSTNnetwork using circuit-switched communications protocols and with an MGW7 and MGW 47 (for example, through employment of a device controlprotocol, such as the Megaco protocol), and with Home LocationRegisters/Visiting Location Registers (for example, using TIA/EIA-41protocols).

[0022] The LMSDS 11 includes network entities HLRe 15, which functionsas a home location register emulator, and MSCe 17, which functions as amobile switching control emulator. Network 1, with its included networkentities, and their associated reference points, comprises a wireless PSnetwork. Network 2, with its included network entities, and theirassociated reference points, also comprises a wireless PS network. Theentities HLRe's 15, 41, MSCe's 17, 45 and MGW's 7, 47, and referencepoints/interfaces 38,39, yy, and zz can employ communication protocolsbased on existing open-standards.

[0023] The MSCe 17 and MSCe 45 further have an interworking function orinterworking engine. Generally, the interworking engine is employable asa command center mapping of routing information within the MSCe whentransmitting data from a circuit-switched network to a packet-switchednetwork. For the purposes of mapping, there can be an interworkingengine in the MSCe's of both network 1 and network 2.

[0024] The network architecture model depicted in FIG. 1 is a functionalblock diagram. As used herein, a network entity represents a group offunctions, not necessarily a physical device. The physical realizationis an implementation issue. A manufacturer can choose a physicalimplementation of network entities, either individually or incombination, as long as the implementation meets the functionalrequirements. Sometimes, for practical reasons, the functional networkentity is a physical device. The Mobile Station (MS) is an example of afunctional entity that is also a physical device.

[0025] As used herein, a reference point is a conceptual point thatdivides two groups of functions. It is not necessarily a physicalinterface. A reference point can become a physical interface when thenetwork entities on either side of it are contained in differentphysical devices. A reference point or interface could be standardized,but not necessarily. A reference point exists when two network entitiesare interconnected through one signaling or bearer stream point.Reference points identify that a logical relationship exists between twonetwork entities. An interface is generally defined across a specificreference point by defining the protocol and data exchanged between theentities. One or more interfaces can be defined for each reference pointin the LMSDS system. The points/interfaces 38, 39, yy, zz can employcommunications protocols based on existing open-standards.

[0026] The LMSDS system 11 comprises a collection of the networkentities, the HLRe 15 and the MSCe 17. The LMSDS system 11 can supportinterfaces using open-standards signal communications protocols at theindicated reference points. These can be the ANSI-41 network signaling,PSTN signaling, media gateway signaling, radio access network signaling,and LMSDS system signaling.

[0027] The LMSDS system 11 has the capability of processing mobilitymanagement and call control messages from the ANSI-41 network and mobilestations for mobile originated and mobile terminated calls. It controlsthe establishment of voice bearers between access network 42 and MGW 7,and between access network 43 and MGW 47. The LMSDS 11 and LMSDS 12 alsoare responsible for establishment of voice bearers between MGW 7 andPSTN 44 and emulate the functionality of the HLRe's 15 and 41,respectively. If requested, the LMSDS 11 performs authentication ofmobile stations, and performs call delivery to another LMSDS 12 ofnetwork 2 across reference point zz, using an open-standards PSprotocol, such as SIP.

[0028] The LMSDS system 11 and 12 perform the call control, mobilitymanagement and service management functions to provide support fornon-PS (that is, legacy) mobile station networks. The LMSDS systems 11and 12 are responsible for the control of call origination and calltermination of both the circuit and packet switched networks. The LMSDS11 and 12 terminate the user-network signaling and convert it into theappropriate network-network signaling. The LMSDS 11 and 12 also controlthe connections for bearer channels in MGW 7 and connections to a basestation controller (BSC) (not shown) in the access network 42.

[0029] The MSCe 17 is responsible for one or more call controlfunctions. The MSCe 17 uses PS signaling to control the MGW 7 acrossreference point 39 and to allow the MGW 7 to communicate with MGW 47 ofnetwork 2 across reference point/interface yy. The MSCe 17 translates areceived E. 164 number into an IP address when IP bearer is to be used.

[0030] The HLRe 15 is a network entity that supports non-PS Terminals(legacy MS's) in a PS network. The HLRe 15 can have a PS signalinginterface. The HLRe 15 supports roaming to the other PS networks. TheHLRe 15 also manages the subscriber profile for both voice services (forexample, Call Forwarding, Three Way Calling, Message WaitingNotification) and data services (for example, Priority). Subscriberprofile information can be accessed from the HLRe 15 or can bedownloaded to a serving system as needed.

[0031] The HLRe 15 manages subscriber location and/or accessibilityinformation. This includes updating the dynamic subscriber informationdatabase with current domain information (for example, MSCe address) andwith MS status information (for example, SMS pending flag). The HLRe 15also interacts with the location database to update or retrieve currentlocation information.

[0032] The LMSDS 11 supports the following interfaces or referencepoints. The MGW to radio access network circuit data bearer (27) issupported. The MGW to PSTN bearer (34), MSCe 17 to MGW 7 signaling (38)and media gateway to media gateway PS bearer (yy) interface or referencepoints are also supported.

[0033] The MGW 7 is employable to provide one or more packet signalswitching capabilities. In FIG. 1, the MGW can receive bearer channelsfrom the PSTN on interface 34, bearer channels from the radio network oninterfaces 27 and media streams from a packet network on interface yy.The MGW 7 also supports voice and circuit data media streams on thesenetwork terminations, provides switching of the bearer channels byconnecting media streams from one set of network terminations to anotherset of network terminations, and converts media in one type of networktermination to the format required in another type of networktermination.

[0034] Open-standards signal communications protocols can be used acrossits reference points/interfaces. These include, for example, the mediagateway control protocol (Megaco) and SIP, a packet-switched datacontrol protocol. Using these standardized reference point/interfacesallow the interworking function to communicate with the PSTN and the MGWof the first mobile network with the entities of the second mobilenetwork in a standardized manner using packet switched protocol.

[0035] Media gateway control protocol, also known as H.248 or Megaco, isan open-standards protocol for handling the signaling and sessionmanagement needed during a multimedia conference. Megaco can be used tocommunicate signals between the MSCe and the MGW.

[0036] Session initiation protocol (SIP) is a request-response PSprotocol that establishes call parameters at either end of thecommunication, and handles call transfer and termination. SIP can beemployed when communicating between the MSCe 17 and the MSCe 45; thatis, from the first mobile network to the second mobile network, alonginterface zz. SIP is an open-standards PS protocol and participants areidentified by SIP URLs. Requests can be sent through any transportprotocol, such as UDP, SCTP or TCP. SIP determines the end system to beused for the session, the communication media and media parameters, andthe called party's desire to engage in the communication. Once these areassured, SIP establishes call parameters at either end of thecommunication, and handles call transfer and termination. SIP is alsoused for initiating an interactive user session that involves multimediaelements such as video, voice, chat, gaming, and virtual reality.

[0037] Like HTTP or SMTP, SIP works in the Application layer of the OpenSystems Interconnection (OSI) communications model. The Applicationlayer is the level responsible for ensuring that communication ispossible. SIP can establish multimedia sessions or Internet telephonycalls, and modify or terminate them. The protocol can also inviteparticipants to unicast or multicast sessions that do not necessarilyinvolve the initiator. Because the SIP supports name mapping andredirection services, it makes it possible for users to initiate andreceive communications and services from any location, and for networksto identify the users wherever they are.

[0038] Interface yy is a PS bearer interface between MGWs operatingusing IP. Interface 39 is used for the MGW 7 to communicate to the MSCe17. Interface 39 provides PS signaling, control bearer resourceassignment and bridging from the MSCe 17 to the MGW 7.

[0039] Turning now to FIG. 2, illustrated is an OSI protocol stack forinterface zz. Generally, the interworking engine of the MSCe 17 allowsfor the communication of signals from the interface 13 through theinterface zz. Interface zz provides PS signaling control employed by theinterface yy. This interface is between MSCes. Interface zz is asignaling interface that is based on SIP-T as defined in IETF-2 andIETF-3. SIP can be employ either TCP as defined in IETF-5, UDP asdefined in IETF-6 or SCTP as defined in IETF-4. IP as defined in IETF-7is used as the network protocol. In FIG. 2, layer 1 represents thephysical layer of the OSI protocol stack, and can be a wire, or can bewireless. Layer 2 represents data link layer. Layer 3 represents thenetwork layer. It is within the layer 3 that the SIP is employed.

[0040] With reference now to FIG. 3, an example of call clearing thathas been initiated by an MS will be described. In this example, an MS isoutside the serving area of the MSCe 17 where the call originated. Inthe following, there are two PS core networks, a first network 1 and asecond network 2. In this example, the first network 1 is theoriginating network (for example, the network receiving the call fromthe circuit switched (CS) network, such as the PSTN 44 in this example)and the second network 2 is the serving network (for example where thecall is transmitted to BS), and a third network, which has a CS core,such as the PSTN 44 or other CS core network.

[0041] In step 301, the BS sends a Clear Request message per a PSprotocol, can be a per a standard protocol, such as 3GPP2, to a servingMSCe. This message acts as a trigger to initiate a sequence of steps toclear the call transaction. It is assumed that, prior to this step, anMS (not shown) was in communication with the BS 49. The MS may also havetransmitted a signal to the BS 49 to request that it initiate the callclearing sequence (such as by pushing “end”). The BS 49 may alsoinitiate a Clear Request on its own (if a signal is lost, and so on.) orfor other reasons. However, the reason the BS sends the Clear Requestmessage is not material to the present invention.

[0042] In step 302, a Serving MSCe 45 sends a PS protocol message, whichin this example is a Clear Command message per 3GPP2, to the BS toinstruct the BS to release the associated dedicated resource, such as,the communication channel between the BS and the MS or other device.

[0043] As shown in step 303, the receipt of a Clear Request message bythe Serving MSCe 45 from the BS 49 also triggers the serving MSCe 45 tosend the serving MGW 47 (of the same network) message to clear thenetwork communication channel using a PS protocol message. In thisexample, the PS protocol message is a Megaco device control formatmessage consisting of two SUBTRACT commands per IETF-8. The firstSUBTRACT command removes a termination to the BS communication channel(for example, DS0 on T1 or E1 line). The second SUBTRACT removes atermination for a bearer channel of the serving network to theoriginating using RTP.

[0044] In step 304, the sServing MGW 47 replies to the Megaco or otherPS protocol message with a Reply acknowledging that the bearer channelhas been terminated. In this example, this message is a Reply perIETF-8.

[0045] In step 305, the Serving MSCe 45 sends a message to theOriginating MSCe 17 using a PS protocol, which is a BYE per IETF-2message, including an REL per SS7 encapsulated within it.

[0046] In step 306, upon receiving a BYE message, an Originating MSCe 17sends a message using a CS protocol to the PSTN 44 (or other CSnetwork), which is a REL message per SS7.

[0047] In step 307, upon receiving the BYE message, the Originating MSCe17 also sends the originating MGW 7 of its network a PS protocol devicecontrol format message, which is which in this example, is a Megacomessage consisting of two SUBTRACT commands per IETF-8. The firstSUBTRACT command removes a termination to a PSTN communication channel(for example, DS0 on T1 or E1 line). The second SUBTRACT removes atermination for a bearer channel using RTP.

[0048] In step 308, the originating MGW 7 replies to the PS protocolmessage (that is, the Megaco SUBTRACT commands, with a PS protocolReply, which can be a Megaco Reply message.

[0049] In step 309, the CS network, in this case the PSTN 44, sends a CSprotocol message, which is a RLC per SS7, to the Originating MSCe 17.Note this message can be received by an Originating MSCe 17 anytimeafter a REL message is sent (see Step 306). It is not necessary to waitfor steps 307 and 308 to be performed.

[0050] In step 310, the BS 49 of the Serving Network 2 returns a PSprotocol message, which is a Clear Complete message per 3GPP2-3, to theServing MSCe 45. In response, the Serving MSCe 45 releases theunderlying transport connection. Note this message can be received by aServing MSCe 45 anytime after Step 302. It is not necessary to wait forsteps 303 to 309 to be performed.

[0051] In step 311, upon receiving the PS protocol message, that is, theReply message from the originating MGW 7 and upon receiving the RLCmessage from a PSTN 44, the originating MSCe 17 sends a 200 OK messageper IETF-2 to Serving MSCe 45. This message acknowledges the BYE message(see Step 305).

[0052] With reference now to FIG. 4, this scenario describes callclearing that has been triggered by a CS protocol request from the CScore network, such as the PSTN 44 in this example. In this example, thePSTN 44 sends an SS7 REL message, which is a CS protocol message, to theoriginating MSCe 17. In this example, the MS is outside the serving areaof the MSCe 17 where a call originated, but this need not be the case.

[0053] In step 401, a CS protocol message is sent to the originatingMSCe 17, which is a REL message per SS7. This initiates or triggers theprocess of clearing the call.

[0054] In step 402, the originating MSCe 17 sends a PS protocol message,which is a SIP BYE message per IETF-2, to a Serving MSCe 45. This PSprotocol message also includes a CS protocol message, which is a RELmessage per SS7 encapsulated within it. That is, the SS7 signal messageis mapped to the PS protocol signal message by a mapper. Accordingly, bybeing able to handle both CS protocol and PS protocol messages, theMSCe's 17 and 45 perform interworking functions between the two types ofcore network, that is each acts as an interworking engine.

[0055] In step 403, upon receiving the BYE message, the serving MSCe 45sends a PS protocol message, which is a Service Release message per3GPP2-3, to the BS 49 to instruct a BS 49 to release the call controltransaction associated with a service.

[0056] In step 404, the BS 49 releases a service option connectionidentifier, a terrestrial circuit, if allocated for the associatedservice, and send a PS protocol message, which is a Service ReleaseComplete message per 3GPP2-3, to the serving MSCe 45.

[0057] In step 405, upon receiving the BYE message, the serving MSCe 45sends the serving MGW 47 a PS protocol device control format message toremove terminations. This PS protocol message is a Megaco messageconsisting of two SUBTRACT commands per IETF-8. The first SUBTRACTcommand removes a termination to a BS communication channel (forexample, DS0 on T1 or E1 line). The second SUBTRACT removes atermination for a bearer channel using RTP.

[0058] In step 406, the serving MGW 47 replies to the Megaco messagewith a PS protocol device control format message, which is a Replymessage per IETF-8.

[0059] In step 407, upon receiving the Service Release Complete message(see Step 404) and upon receiving a Reply message (see Step 406) theServing MSCe 45 sends a 200 OK message to the originating MSCe 17. Thismessage acknowledges the BYE message (see Step 402).

[0060] In step 408, after sending the BYE message, the originating MSCe17 sends the Originating MGW 7 a PS protocol message in device controlformat, which is a Megaco message consisting of two SUBTRACT commandsper IETF-8. The first SUBTRACT command removes a termination to a PSTNcommunication channel (for example, DS0 on T1 or E1 line). The secondSUBTRACT removes a termination for a bearer channel using RTP.

[0061] In step 409, the originating MGW 7 replies to a Megaco messagewith a PS protocol, in device control format, which is a Megaco Replymessage.

[0062] In step 410, the originating MSCe 17 sends a CS protocol message,which is an RLC message per SS7, to the CS network, in this case, thePSTN 44, to cause the PSTN 44 to clear the call. This completes the callclearing process.

[0063] Of course, the present invention is not limited to any particularcommunication technology for the PS network or RAN. For example, thepresent invention is applicable to CDMA, GSM, TDMA, UMTS communicationtechnology and wired systems as well.

[0064] It is understood that the present invention may take many formsand embodiments. Accordingly, several variations may be made in theforegoing without departing from the spirit or the scope of theinvention.

[0065] Having thus described the present invention by reference tocertain of its preferred embodiments, it is noted that the embodimentsdisclosed are illustrative rather than limiting in nature and that awide range of variations, modifications, changes, and substitutions arecontemplated in the foregoing disclosure and, in some instances, somefeatures of the present invention may be employed without acorresponding use of the other features. Many such variations andmodifications may be considered obvious and desirable by those skilledin the art based upon a review of the foregoing description of preferredembodiments. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theinvention.

1. An interworking engine operable in a first PS network for clearing acall between a second PS network and a CS network, comprising: a firstinput employable to receive a first CS protocol signal from the CSnetwork to trigger initiation of a call clearing action; a mapperemployable to map the first CS protocol signal into a first PS protocolsignal relating to clearing a call; a first output employable totransmit the first PS protocol signal relating to clearing the call toan interworking engine of the second PS network; a second outputemployable to transmit a second PS protocol signal, in device controlformat, to a media gateway requesting subtraction of a trunk line andsubtraction of an RTP; a second input employable to receive a first PSprotocol response from the interworking engine of the second PS networkto the first PS protocol signal; a third input employable to receive asecond PS protocol response from the media gateway, in device controlformat, to the second PS protocol signal; a mapper employable to map aPS protocol message relating to clearing the call into a CS protocolformat; and a third output employable to transmit a second CS protocolmessage to the CS network relating to clearing of the call.
 2. Theinterworking engine of claim 1, wherein the first CS protocol signalcomprises SS7 protocol.
 3. The interworking engine of claim 1, whereinthe first PS protocol signal comprises SIP.
 4. The interworking engineof claim 1, wherein the first PS protocol response comprises SIP.
 5. Theinterworking engine of claim 1, wherein the second PS protocol signalcomprises Megaco protocol.
 6. The interworking engine of claim 1,wherein the second PS protocol response comprises Megaco protocol. 7.The interworking engine of claim 1, wherein the second CS protocolmessage response comprises SS7 protocol.
 8. A media gateway in a firstPS network functioning as a bearer for communications between it and asecond PS network and between it and a CS network, comprising: a firstinterface employable to receive a PS protocol signal, in device controlformat, from an interworking engine of the first PS network requestingsubtraction of a trunk line and subtraction of an RTP; and a secondinterface employable to transmit a PS protocol response to the PSprotocol signal from the interworking engine of the first PS network. 9.The media gateway of claim 8, wherein the PS protocol signal comprisesMegaco protocol.
 10. The media gateway of claim 8, wherein the PSprotocol response comprises Megaco protocol.
 11. The media gateway ofclaim 9, wherein the PS protocol comprises a Megaco subtract trunkcommand and a subtract RTP command.
 12. The media gateway of claim 10,wherein the PS protocol response comprises a Megaco Reply.
 13. Atelecommunications system having at least a first PS network and asecond PS network and a third circuit-switched core network, and asystem for terminating a legacy domain circuit-switched communicationupon receipt of a trigger signal requesting termination ofcommunication, the system for terminating a legacy domaincircuit-switched communication, comprising: a first functional and asecond functional entity in each of said first and second networks; saidfirst functional entity and said second functional entity of said firstnetwork including means for communicating signals over an interfaceusing a PS protocol; said first functional entity and said secondfunctional entity of said second network including means forcommunicating signals over an interface using a PS protocol; said firstfunctional entity of said first network having means for communicatingpacket data to and from said first functional entity of the secondnetwork; said second functional entity of said first network havingmeans for communicating a PS protocol signal to said second entity ofsaid second network; and said second functional entity of said secondnetwork further including means for communicating a circuit-switchedprotocol signal to and from said third circuit-switched protocol corenetwork to terminate said circuit-switched communication.
 14. The systemdefined in claim 13, wherein said second functional entity of said firstnetwork includes means for communicating signals to and from a publicswitched telephone network using a circuit-switched protocol.
 15. Thesystem defined in claim 13, wherein said first functional entity is amobile gateway.
 16. The system defined in claim 13, wherein said secondfunctional entity is a mobile switching center emulator.
 17. The systemdefined in claim 13, wherein said second network entity of each of saidfirst and second networks includes means for receiving a trigger signalrequesting termination of a circuit-switched communication.
 18. Thesystem defined in claim 17, wherein said trigger signal is a clearsignal from an access network.
 19. The system defined in claim 17,wherein said trigger signal is a service release signal.
 20. The systemdefined in claim 13, wherein said means for said second network entityof said first network to communicating signals to and from said secondnetwork entity of said second network includes a Megaco subtract trunksignal and a subtract RTP signal.
 21. The system defined in claim 13,wherein said means for said second network entity of said first networkto communicating signals to and from said second network entity of saidsecond network includes a Megaco reply signal.
 22. The system defined inclaim 13, wherein said means for communicating signals to and from saidthird circuit-switched protocol network uses an open-standardscircuit-switched communications protocol.
 23. The system defined inclaim 22, wherein said open-standards circuit-switched communicationsprotocol includes an SS7 REL signal.
 24. The system defined in claim 22,wherein said open-standards circuit-switched communications protocolincludes an SS7 RLC signal.
 25. The system defined in claim 13, whereinsaid means for said second functional entity and of said first networkto communicate signals to and from said second functional entity of saidsecond network comprises an SIP BYE signal.
 26. The system defined inclaim 13, wherein said means for said second functional entity and ofsaid first network to communicate signals to and from said secondfunctional entity of said second network comprises an SIP OK signal. 27.In a telecommunications system having at least a first PS network and asecond PS network and a third circuit-switched core network, each ofsaid first and second networks having first and second functionalentities, a method for terminating a legacy domain circuit-switchedcommunication upon receipt of a trigger signal requesting termination ofcommunication, comprising the steps: communicating a PS protocol signalbetween said first functional entity and said second functional entityof said first network over an interface; communicating a PS protocolsignal from said second functional entity to said first functionalentity of said first network over an interface to control termination ofcommunication of packet data by said first functional entity of saidfirst network; communicating a PS protocol signal from said firstfunctional entity of said first network to said first functional entityof said second network requesting termination of the communication ofpacket data by said first functional entity of said second network;communicating a PS protocol signal from said second functional entity tosaid second functional entity of said first network over an interface tocontrol termination of communication of packet data by said firstfunctional entity of said second network; and communicating acircuit-switched protocol signal from said first functional entity ofsaid second network to said third circuit-switched protocol core networkto terminate communication with said third network.
 28. The methodsystem defined in claim 27, wherein said third network is a publicswitched telephone network.
 29. The system defined in claim 27, whereinsaid first functional entity is a mobile gateway.
 30. The system definedin claim 27, wherein said second functional entity is a mobile switchingcenter emulator.
 31. The system defined in claim 27, wherein said secondfunctional entity of said first network transmits a signal to the secondfunctional entity network entity of said second network in response toreceiving a trigger signal requesting termination of a circuit-switchedcommunication.
 32. The system defined in claim 31, wherein said triggersignal includes a clear signal.
 33. The system defined in claim 31,wherein said trigger signal includes a service release signal.
 34. Thesystem defined in claim 27, wherein said signals transmitted from saidsecond network entity of said first network to said second networkentity of said second network include a Megaco subtract trunk signal anda subtract RTP signal.
 35. The system defined in claim 27, wherein saidsignals transmitted from second network entity of said first network tosaid second network entity of said second network include a replysignal.
 36. The system defined in claim 13, where said communicating ofsignals to and from said third circuit-switched protocol network isperformed using an open-standards circuit-switched communicationsprotocol.
 37. The system defined in claim 25, wherein saidopen-standards circuit-switched communications protocol includes an SS7REL signal.
 38. The system defined in claim 36, wherein saidopen-standards circuit-switched communications protocol includes an SS7RLC signal.
 39. The system defined in claim 13, wherein said signaltransmitted between said second functional entity of said first networkto and from said second functional entity of said second networkcomprises an SIP BYE signal.
 40. The system defined in claim 13, whereinsaid signal transmitted from said second functional entity of said firstnetwork to said second functional entity of said second networkcomprises an SIP OK signal.